I know that perpetual motion machines can't work because of friction, but intuitively I thought that Escher's waterfall (https://cdn.churchm.ag/wp-content/uploads/2011/04/waterfall-illusion-e1302170121549.jpg) couldn't work because of the absence of external energy. I can't see where friction prevents this process from working. Any ideas? Thanks in advance and have a good day :)


closed as unclear what you're asking by sammy gerbil, stafusa, Cosmas Zachos, Chris, valerio Feb 19 '18 at 9:01

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Escher's waterfall doesn't work because you can't fall off a cliff, then go downhill and end up where you started. It's geometry, not physics.

  • $\begingroup$ Better repeat the subject, in your last sentence. At first I took it reverse way, wanted to correct you by saying Escher waterfall is art and geometry not physics :) than realise what you meant. $\endgroup$ – Alchimista Feb 17 '18 at 11:46
  • $\begingroup$ Okay but I need an answer based on physics. $\endgroup$ – musicinmyheart Feb 17 '18 at 12:28
  • $\begingroup$ @musicinmyheart well you could argue that geometry (since GR) is physics.... $\endgroup$ – lalala Feb 17 '18 at 13:00
  • 2
    $\begingroup$ You can recouch it in physics terms: gravity is a conservative force and so it can't decrease all the way around a loop. $\endgroup$ – Chris Feb 17 '18 at 22:31

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